How useful are the old fashioned data flow diagrams in today’s world, in particular how useful are they in demonstrating process flow? They showed the relationship between external entities (actors), functions/processes, data stores and data flows.
Here’s some links, including, wikipedia: Data Flow Diagrams, which has some further reading; I also found this article where the abstract talks about the evolution from DFD to more object friendly techniques. The two techniques fashionable in the ’80s were Yourden and Gane & Sarson. Very similar techniques, just different symbols.